Highly tunable hole quantum dots in Si-Ge shell-core nanowires

In this thesis, we fabricate silicon-germanium core-shell nanowire on bottom gate devices. Using these gates, we create electrostatically defined, fully tunable single
and double quantum dots. In a previous device we were unable to reach the single hole regime due to quantum dots forming between adjacent gates. In this work, we show two routes for solving this problem: the first is to reduce the pitch from 100 to 40 nm and embedding 60 nm pitch gates. The latter has a larger pitch but results in a more homogeneous surface for the deposited nanowires. Both approaches have yielded functional devices although only one device with gate defined quantum dots was realised on the 60 nm embedded gates. On this device, two adjacent gates
do not induce a quantum dot but instead function as one bigger tunnel barrier. Intentional single and double quantum dots were realised using a total of 3 or 5 adjacent gates respectively. At 4.2 K, a region of regular sets of bias triangles were observed indicating a clean system. The single hole regime has not been observed due to local disorder causing fluctuations in the valence band edge.